Hardly decomposable substances such as dioxins known as the substance harmful to human body, i.e., hardly decomposable harmful substances are discharged into natural environment from incinerator for urban waste or industrial waste and various combustion facilities or machineries.
Moreover, various kinds of organic compounds in manufacturing process of chemical substance which will unintentionally give bad influence upon environment are discharged causing big social problems. Although the generation mechanism of chloridized aromatic compound such as dioxins, chlorophenol, chlorobenzene is not apparent, it is said that they generate in a treating process for wasting gas of low temperature in the presence of nonflammable carbon, air, moisture, inorganic chlorine, etc.
As sources of releasing wastewater containing these compounds, chloride base bleach facilities in Kraft pulp production plant, decomposition facilities of wasted PCB or processed PCB, cleaning equipment for PCB contaminant or PCB processed product, cleaning equipment modifying fusion furnace to provide for manufacture of aluminum and aluminum alloy, wet type dust collection facilities, waste pit discharging sewage, etc., are known. Namely, a process using compounds containing chlorides has probability of generating the foregoing wastewater.
Further, standard of aqueous environment pollutant was revised by Ministry of Environment and as a result, organic compounds such as trichloroethylene, tetrachloroethylene, PCB were newly added to object substance of the environmental quality standard in which heavy metals were main entity until then. It is probable that a slight amount of harmful substance such as organophosphorus compound, PCB, trichloroethylene, dioxines, bisphenols and so on is contained in industrial wastewater, in addition to oils, chemical oxygen demand (COD), biochemical oxygen demand (BOD) and suspended substance (SS).
Conventionally, technologies for decomposing hardly decomposable harmful substances in wastewater which removes the hardly decomposable harmful substances as much as possible from the object wastewater containing the hardly decomposable harmful substances by means of a filtration equipment, a membrane separation method, etc., have been developed (refer to, for example, Japanese Unexamined Patent Application Laid-Open No. Hei 11-99395).
For the purpose of treating wastewater containing the hardly decomposable harmful substances as mentioned above, a filtration treatment, a bio-organic treatment or so is carried out as a pretreatment and then, an ozone treatment, an ultraviolet irradiation treatment, a catalyst treatment, an activated carbon treatment or so is carried out as an aftertreatment. As thus described, it was necessary to decompose and remove the hardly decomposable harmful substances spending great labors and materials in the past.
Further, giving the ultraviolet irradiation treatment in example, it is a technology which can take advantage only about the reaction system in which the ultraviolet ray can transmit, and there is a problem that it cannot take advantage about solid or a liquid containing solid. Furthermore, it is necessary for the hardly decomposable harmful substances removed by the pretreatment to be processed specially into harmless in order to prevent the secondary contamination.
Accordingly, development of a decomposition treatment technology for these hardly decomposable harmful substances efficiently and without contaminating human body or surrounding environment again is eagerly desired.